Question

Calculati suma S= (96,34+x)+(86,34+x)+...+(16,34+x), unde x=3,66

Answer 1

$16,34+x=16,34+3,66=20. \\ \\ S=(80+16,34+x)+(70+16,34+x)+(60+16,34+x)+...+ \\ \\ +(16,34+x)= \\ \\ =(80+20)+(70+20)+(60+20)+...+(10+20)+20= \\ \\ =9 \cdot 20 + (80+70+60+...+10)= \\ \\ =180+10(8+7+6+...+1)= \\ \\ =180+10 \cdot \frac{8 \cdot 9}{2}= \\ \\ =180 +5 \cdot 8 \cdot 9=$

$=540$